An Oscar-bound performance delivered on a silver platter, “Darkest Hour” makes up for a lot of the money gigs Gary Oldman has done in recent years, slithering through one action movie after another, portraying a Eurotrash or Slavic adversary wielding a slippery combination of dialects like switchblades.

An actor needs to eat, of course. But in “Darkest Hour,” director Joe Wright’s posh dramatization of a few key weeks in the life of British Prime Minister Winston Churchill, Oldman — barely recognizable, supremely vital — isn’t just eating; he’s feasting.

Many of his peers consider Oldman to be the finest living screen actor, which may surprise moviegoers too young to remember “Sid and Nancy” or “Prick Up Your Ears,” or those who’ve missed his recent stealth achievements, notably in “Tinker, Tailor, Soldier, Spy.” Spymaster George Smiley was, in Oldman’s own description, a “sitting-down role,” reliant on poker-faced minimalism. “Darkest Hour” pulls from both extremes of Oldman’s prodigious but often unexploited skill set, the subtlety as well as the flamboyance.

The famous Churchill jowls, the hairline in retreat, the larger-than-life John Bull countenance all require an actor (who bears no resemblance to his subject) be able to make himself at home underneath one of the most exquisitely detailed makeup jobs in modern movies. This visual realization of Churchill owes a huge debt to prosthetics, makeup and hair designer Kazuhiro Tsuji, a master of his craft. Woody Harrelson may have spent a similar number of hours in the chair while filming “LBJ,” but that ended up being a film about a president at war with his own latex. “Darkest Hour” works on a higher plane. The top-of-the-line visual concealment allows Goldman to concentrate on what matters: finding the physical details, activating the Churchill speeches, putting all his evident research to good use.

It’s a lovely performance, and while the movie has its phony aspects, it’s never less than entertaining. “Darkest Hour” depicts Churchill’s life in 1940, as the newly installed prime minister succeeds Conservative Party statesman Neville Chamberlain (Ronald Pickup, glowering over his mustache) amid the Nazi ravaging of Europe. As Foreign Secretary Viscount Halifax, Chamberlain’s partner in Third Reich appeasement, Stephen Dillane keeps his chin tucked low while playing up, slyly, the Elmer Fuddian w-for-r consonants. Dillane shares some screen time with Ben Mendelsohn’s King George VI (the one Colin Firth played in “The King’s Speech”), and when they’re together, the air is thick with royal privilege. “Darkest Hour” benefits from some exceedingly witty actors, including Kristin Scott Thomas as Clementine Churchill (sadly marginalized and somewhat neutralized here; theirs was not a placid marriage). Everyone’s having a discreet ball portraying the private side of highly public figures in crisis.

Screenwriter Anthony McCarten swiftly introduces Churchill’s new personal secretary, Elizabeth Layton (Lily James, the quintessence of British pluck). “He mumbles,” she’s told early on regarding Churchill, “so it’s impossible to catch everything.” Through Layton, the audience is whisked into Churchill’s inner circles. The film burrows into the machinations of the war cabinet, as Churchill and his skeptical partners in policy debate the practicality and wisdom of peace talks with Hitler, urged by Halifax, with Mussolini acting as go-between.

In part “Darkest Hour” concerns how Churchill hit upon Operation Dynamo as a way of pulling off the astonishing evacuation of British troops stranded at Dunkirk, across the English Channel. In the recent Dunkirk movie sweepstakes, director Wright has placed first and third, first being “Atonement” (featuring a grandiose, show-offy one-take panorama of the French coastal evacuation) and the third being “Darkest Hour.” The one in the middle, Christopher Nolan’s “Dunkirk,” took you there, to the beach and to the skies, and put you through the wringer. “Darkest Hour” serves as the strategy- and process-focused bookend to Nolan’s film.

Director Wright’s penchant for theatrics suits the highly theatrical Churchill nicely. There are images of Oldman’s Churchill, isolated in an elevator or a bathroom, when the screen becomes an ink-black diorama surrounding a lonely, fraught man of destiny. Less effectively, Wright over-relies on dizzying practical and digital overhead shots of a teeming, fractious Parliament, for example, or (unforgivably) a bomb’s-eye-view perspective as the Luftwaffe attack British forces.

The most blatant narrative invention in “Darkest Hour” finds Churchill bailing out of his car amid heavy London traffic and taking the underground. He’s on the verge of a century-altering decision: Should Britain agree to compromise with the Axis powers, or fight the good fight? Churchill chats with a carful of ordinary working-class London residents, all stunned and thrilled to be in the company of the instantly recognizable prime minister. It’s like a scene out of Shakespeare’s “Henry V,” with the king commiserating with his soldiers the night before the battle. And it’s fishy; it’s balderdash. Yet Oldman’s wonderful here, delighting in the change of key. The scene may be balderdash, but it serves a dramatic purpose.

And yes, “Darkest Hour” provides another kind of service. It’s a reminder of the power of oratory. It’s an illustration of the value and necessity of working with ideological opposites in the spirit of bipartisanship, sometimes against a larger enemy. And it’s a nostalgic glimpse of political life before Twitter, a time before our own, when world leaders (one in particular) fiddle while nations burn.